1. Field of the Invention
This invention relates to a method of producing a polycarbonate composition having excellent weatherproof properties by the phosgene process.
2. The Prior Art
It has been known heretofore to produce high molecular polycarbonate compositions by the method which comprises reacting a dioxy compound such as bisphenol A with phosgene to prepare carbonate oligomer and then condensing the so-obtained oligomer to polymerize the same. Although this polycarbonate has excellent properties in heat resistance and impact strength (or impact resistance) it is poor in weatherproof property. Thus, it shows the defect that cleavage of its carbonate ester bonds occurs upon exposure to ultraviolet rays and its molecular weight is lowered.
In order to improve this defect, according to the prior art, a small amount of ultraviolet absorbing compound was added to the polycarbonate powder and subsequently the mixture was subjected to extrusion molding to make pellets. This prior art method, however, has the following disadvantages:
(1) It is very difficult to keep a fixed content of said ultraviolet absorbing compound because it vents itself up during extrusion molding and is reduced in its quantity; PA1 (2) Only a small amount of the compound can be added because of its characteristic yellow color; and PA1 (3) Since the ultraviolet abosrbing compound is added in the form of a monomer, the physical properties of the resultant polycarbonate composition are inferior.